Search results for "Enthalpy"
showing 10 items of 199 documents
Protonation thermodynamics of 2,2'-bipyridyl in aqueous solution. Salt effects and weak complex formation
1993
Abstract Protonation constants of 2,2'-bipyridyl (bipy) have been determined potentiometrically, using (H + )-glass electrode, in different aqueous media (alkali and alkaline earth chlorides, tetramethylammonium chloride and tetramethylammonium iodide) at different temperatures and ionic strengths. The differences in log K H values are explained using a complex formation model. Formation thermodynamic parameters are given.
Thermodynamic parameters for the formation of glycine complexes with magnesium(II), calcium(II), lead(II), manganese(II), cobalt(II), nickel(II), zin…
1995
Abstract Protonation constants and Mg 2+ , Ca 2+ , Pb 2+ , Mn 2+ -, Co 2+ , Ni 2+ , Cu 2+ , Zn 2+ and Cd 2+ glycine complex formation constants have been determined in different aqueous media at different temperatures. Salt effects are explained by a complex formation model which takes into account the formation of weak species. From the temperature dependence of the formation constants, thermodynamic parameters ΔH θ (and in some cases ΔC θ p ) have been obtained. A rigorous analysis of literature data, together with experimental findings, allows recommended formation parameters, in the ranges 0 ≤ I e ≤ 1 mol l −1 ( I e is the effective ionic strength) and 5°C ≤ T ≤ 45°C, to be obt…
Binding between (Ethylene Oxide)13−(Propylene Oxide)30−(Ethylene Oxide)13 and Sodium Decanoate. Volume, Enthalpy, and Heat Capacity Studies
2002
Volume, enthalpy, and heat capacity of transfer (ΔYt) of (ethylene oxide)13−(propylene oxide)30−(ethylene oxide)13 (L64), at some concentrations, from water to the aqueous sodium decanoate (NaDec) solutions as functions of the surfactant concentration (mS) were determined at 298 K. The copolymer was studied in both the unassociated and associated forms. For a given L64 concentration (mC), the ΔYt vs mS profiles for the volume and the enthalpy are equal but different from that of the heat capacity because the latter contains also the relaxation terms. The experimental data were analyzed by assuming the distribution of L64 between the aqueous and the micellar phases and the shift of micelliza…
Heat Capacity of Transfer of (Ethylene oxide)13-(propylene oxide)30-(ethylene oxide)13 from Water to the Aqueous Anionic Surfactant Solutions at 298 …
2004
Heat capacities of transfer (ACpt) of unimeric (ethylene oxide)(13)-(propylene oxide)(30)-(ethylene oxide)(13) from water to the aqueous surfactant solutions as functions of the surfactant concentrations (m(S)) were determined at 298 K. The surfactants investigated are sodium hexanoate, sodium heptanoate, sodium octanoate, sodium undecanoate, and sodium dodecanoate. For short alkyl chain surfactants, the profiles of the DeltaCp(t) versus ms curves show maxima and minima; for long alkyl chain surfactants, the maximum becomes sharper and moved to lower ms values whereas the minimum tends to disappear. These experimental trends are different from those of the enthalpy in agreement with the fac…
Excess enthalpies of solution of primary and secondary alcohols in dodecyldimethylamine oxide micellar solutions
1987
The excess enthalpies of solution with respect to water of some primary and secondary alcohols in dodecyldimethylamine oxide (DDAO) micellar solutions were measured by mixing aqueous solutions of alcohols with surfactant solutions. Standard free energies, enthalpies and entropies were obtained from the distribution of alcohols between aqueous and micellar phases. It is shown that thermodynamics of transfer of secondary alcohols from aqueous to the DDAO micellar phase differ slightly from those of their corresponding primary alcohols, that the additivity rule holds for free energies of transfer and that enthalpy and entropy display convex curves. The present data are compared with those from…
Investigation of the Interpolymer Complex between Hydroxypropyl Cellulose and Maleic Acid-Styrene Copolymer, 1
2004
The hydrogen bonding-interpolymer association of hydroxypropyl cellulose (HPC) with maleic acid-styrene (MAc-S) copolymer has been investigated in dilute aqueous solution by viscometry, turbidimetry and potentiometry. At a mixing ration between MAc-S and HPC of 10:90, the solution exhibits a phase separation upon heating, while for other mixing ration no phase separation could be detected. The stability of the interpolymer complex (IPC) increases as the temperatures rises. The stoichiometry of the IPC, in mole units, was estimated as being MAc-S:HPC=5:2. The thermodynamic functions (enthalpy and entropy) of the complexation process have been determined.
Electrostatic contribution to the interaction of α, β poly (N-hydroxyethyl)-DL-aspartamide with sodium dodecylsulfate micelles
1994
The enthalpic effect due to the interaction between α, β poly(N-hydroxyethyl)-DL-aspartamide (PHEA) and sodium dodecylsulfate (SDS) in aqueous solutions as a function of the surfactant concentration was measured by the calorimetric technique at various NaCl concentrations. A marked influence of the added electrolyte on the PHEA-SDS interaction was observed. An analysis of the experimental enthalpies allows to estimate the electrostatic and the hydrophobic contributions to the enthalpy of interaction between PHEA and SDS micelles. The results were rationalized in terms of effects due to the screening of the charges residing on PHEA and SDS micelles.
A DFT Study of the Conversion of Ptaquiloside, a Bracken Fern Carcinogen, to Pterosin B in Neutral and Acidic Aqueous Medium
2017
The conversion of ptaquiloside (PtQ), a bracken fern (Pteridium aquilinum) carcinogen, to pterosin B (PtB), which is involved in the underlying mechanisms of PtQ genotoxicity and carcinogenicity, has been theoretically studied in aqueous neutral (AN) and acid (AA) media, using DFT methods at the PCM(water)-B3LYP/6-31G(d)//B3LYP/6-31G(d) computational level. The β-elimination of glucose in AN and four reactive channels (A-D) defined by as many protonation sites in PtQ were calculated. Activation enthalpy decreases (from 42.0 to 12.6 kcal mol−1) in AA relative to AN suggesting protic catalysis. The most favoured channel A started with protonation of the tertiary O15 hydroxyl of PtQ and SN1 wa…
Kinetischer nachweis zweier arten von ionenpaaren bei der anionischen polymerisation von styrol in tetrahydropyran
1967
Die durch Na-Naphthalin angeregte Polymerisation des Styrols in THP wurde im Temperaturbereich von -40 bis +50°C kinctisch verfolgt. Die Geschwindigkeitskonstante kw(±) der uber das lonenpaar erfolgenden Polymerisation wurde gemessen, indem die elektrolytische Dissoziation durch Zusatz von Tetraphenylbornatrium unterdruckt wurde. Oberhalb von 20°C ergibt sich bei Auftragung nach ARRHENIUS eine Gerade, aus welcher Aktivierungsenergie Ec und Frequenzfaktor Ac des Kontaktionenpaares zu berechnen sind. Diese Parameter stimmen in guter Naherung mit den E- und A- Werten uberein, die in sehr schwach polaren Losungsmitteln fur die anionische Polymerisation erhalten werden. Unterhalb von +20°C weich…
Molecular dynamics simulation of the surface tension of aqueous sodium chloride: from dilute to highly supersaturated solutions and molten salt
2018
Sodium chloride (NaCl) is one of the key components of atmospheric aerosols. The surface tension of aqueous NaCl solution (σNaCl,sol) and its concentration dependence are essential to determine the equilibrium water vapor pressure of aqueous NaCl droplets. Supersaturated NaCl solution droplets are observed in laboratory experiments and under atmospheric conditions, but the experimental data for σNaCl,sol are mostly limited up to subsaturated solutions. In this study, the surface tension of aqueous NaCl is investigated by molecular dynamics (MD) simulations and the pressure tensor method from dilute to highly supersaturated solutions. We show that the linear approximation of concentration de…